JP6225765B2 - Print control apparatus and print control method - Google Patents

Description

  The present invention relates to a print control apparatus and a print control method.

  The ink jet printer includes a print head having a plurality of nozzles for ejecting ink. In such a print head, some nozzles may be clogged due to an increase in ink viscosity, mixing of bubbles, adhesion of dust or paper dust, and the like. Clogging of the nozzles (ejection abnormality) causes dot omission (a kind of image quality degradation) due to the fact that ink that should be ejected on the recording medium is not ejected.

  As a related technology, an inkjet printer has a normal dither matrix and a non-discharge dither matrix so that white spots (dot missing) due to undischarge are inconspicuous, and selectively based on undischarge position information. A configuration using a dither matrix is known (see Patent Document 1).

JP 2004-202895 A

It has been necessary to prevent deterioration in image quality due to the visual recognition of missing dots as described above.
Although the above document is effective in preventing deterioration of gradation at normal ejection positions other than the non-ejection position, it is insufficient as a configuration in order to make dot missing not conspicuous.

  SUMMARY An advantage of some aspects of the invention is that it provides a print control apparatus and a print control method that can compensate for image quality degradation caused by nozzle ejection abnormality.

  One aspect of the present invention is a print control apparatus that controls a printing process for forming the ink dots on a recording medium by causing the print head to perform a scan in which ink is ejected from the nozzles while moving in a predetermined direction. A discharge control unit that controls the discharge of ink by the nozzle by allocating the pixel constituting the image and determined to discharge or not discharge the ink to the nozzle, and the discharge control unit includes: One time when printing an adjacent pixel row, which is a pixel row adjacent to a pixel row having an abnormal nozzle corresponding pixel that is a pixel assigned to an abnormal nozzle having an abnormality in ink ejection, among the nozzles by a plurality of scans. The degree of dispersion of the dots formed by scanning is determined once when the pixel row that is not the adjacent pixel row is printed by a plurality of times of the scanning. Than the degree of dispersion of the dots formed by scanning reduces.

According to this configuration, the adjacent pixel row adjacent to the pixel row having the abnormal nozzle corresponding pixel to be assigned to the abnormal nozzle has dots formed by one scan included in a plurality of scans for printing the adjacent pixel row. Reproduced on a recording medium in a relatively concentrated state.
For example, by reducing the degree of dispersion of the dots formed by the one scan, at least some of the dots formed by the one scan are in contact with each other.
A plurality of dots formed in such a manner that are concentrated almost simultaneously interfere with each other and tend to spread (easily spread) compared to a case where the dots are formed in a dispersed manner. Accordingly, the missing dot due to the abnormal nozzle in which the ejection abnormality such as clogging is seen is eroded by the dots formed corresponding to the adjacent pixel rows, and as a result, the image quality deterioration due to the ejection abnormality of the nozzle is compensated. .

According to one aspect of the present invention, the lower the print resolution by the scan, the ejection control unit may reduce the number of dots formed in one scan when the adjacent pixel column is printed by a plurality of scans. The degree of dispersion may be reduced.
According to this configuration, even when the printing resolution by scanning is low, dot missing due to an abnormal nozzle can be appropriately compensated for by bleeding of dots formed corresponding to adjacent pixel rows.

In one aspect of the present invention, the ejection control unit is formed in one scan when the adjacent pixel row is printed by a plurality of scans such that the ink is less likely to spread on the recording medium. The degree of dot dispersion may be reduced.
According to this configuration, even when printing on a recording medium in which ink is relatively difficult to bleed, dot missing due to an abnormal nozzle is appropriately compensated for by bleed of dots formed corresponding to adjacent pixel rows. Can do.

In one aspect of the present invention, the print head is capable of ejecting at least the first ink and the second ink having a higher density than the first ink, and the ejection control unit When printing by a plurality of scans, the degree of dispersion of the dots of the second ink formed by one scan is made lower than the degree of dispersion of the dots of the first ink formed by one scan. It is good.
According to this configuration, it is possible to accurately compensate for dot omission due to abnormal nozzles due to bleeding of the high-density second ink that has a high effect of making dot omission inconspicuous.

One aspect of the present invention is that, when the ejection control unit determines ejection of the ink to the abnormal nozzle corresponding pixel, the adjacent pixel row is printed once by the plurality of scans. The degree of dispersion of the dots formed by the scanning is reduced to be lower than the degree of dispersion of the dots formed by one scan when the pixel row that is not the adjacent pixel row is printed by the plurality of scans. Also good.
According to this configuration, when it is determined that ink should be ejected from an abnormal nozzle, that is, when the occurrence of dot missing is a reality, such dot missing is the dot formed corresponding to the adjacent pixel row. It is no longer visible due to bleeding.

  The technical idea of the present invention is not realized only by the print control apparatus described above. For example, a printing control method including processing steps executed by each unit of the printing control apparatus can be regarded as one invention. Further, even if the present invention is realized in various categories such as a computer program that causes a hardware (computer) to execute each step of such a printing control method, and further a computer-readable storage medium that stores the program. Good.

It is a figure showing roughly the device composition concerning this embodiment. It is a figure which illustrates simply the composition of a print head, etc. 6 is a flowchart illustrating print control processing. It is a figure which illustrates the correspondence of the nozzle concerning 1st Embodiment, and a pixel. It is a figure which illustrates a nozzle usage rate regulation mask. It is a figure which illustrates the correspondence of the nozzle concerning 2nd Embodiment, and a pixel. It is a figure for demonstrating an adjacent pixel column.

Embodiments of the present invention will be described in the following order.
1. 1. Outline of device configuration 1. First embodiment Second Embodiment 4. Modified example

1. FIG. 1 schematically shows a configuration of a print control system 1 according to the present embodiment. The print control system 1 includes a printer 20 and a print control device (control device 10) for controlling the printer 20. The control device 10 is a device in which a program for controlling the printer 20 is installed, and is an execution subject of the print control method. The control device 10 is typically a desktop or laptop personal computer (PC), but may be a tablet terminal, a portable terminal, or the like.

  Alternatively, the control device 10, the printer 20, and the like constituting the print control system 1 may be individual devices connected so as to be communicable, or may constitute a single product. For example, the printer 20 may include the control device 10 in a part of the machine body. In this case, the printer 20 including the print control 10 in the machine body corresponds to the print control system 1 or the print control apparatus, and becomes an execution subject of the print control method. In addition, the printer 20 corresponding to the print control system 1 or the print control apparatus may be a multifunction device that also functions as a scanner, a facsimile, or the like.

  In the control device 10, the CPU 12 that is the center of the arithmetic processing controls the entire control device 10 via the system bus. The bus is connected to a ROM 13, a RAM 14, various interfaces (I / F) 19, and the like, and a hard disk drive (HDD) 16, for example, is connected as a storage means. However, the storage means may be a semiconductor memory or the like. The storage means (HDD 16) stores an operating system, application programs, printer driver PD, and the like, and these programs are read out to the RAM 14 and executed by the CPU 12 as appropriate. The CPU 12, ROM 13, and RAM 14 are collectively referred to as a control unit 11. The storage means may store a plurality of nozzle usage rate defining masks 16a, 16b and the like.

The I / F 19 is connected to the printer 20 by wire or wireless. Furthermore, the control device 10 includes a display unit 17 configured by, for example, a liquid crystal display, an operation unit 18 configured by, for example, a keyboard, a mouse, a touch pad, a touch panel, or the like.
Note that the items described as being executed by the control device 10 in the present embodiment may be executed in whole or in part according to a predetermined program on the printer 20 side.

  In the printer 20, the I / F 25 is connected to the I / F 19 on the control apparatus 10 side so as to be able to communicate by wire or wirelessly, and the control unit 21 and the like are connected via a system bus. In the control unit 21, the CPU 22 appropriately reads a program (firmware or the like) stored in the ROM 23 or the like to the RAM 24 and executes predetermined arithmetic processing. The control unit 21 is connected to the print head 26, the head drive unit 27, the carriage mechanism 28, and the feed mechanism 29 to control each unit.

  The print head 26 supplies various inks from a cartridge (not shown) for each of a plurality of types of liquids (for example, cyan (C) ink, magenta (M) ink, yellow (Y) ink, black (K) ink, etc.)). receive. The print head 26 can eject (discharge) ink from a plurality of nozzles provided corresponding to various inks. Of course, the specific types and number of liquids used by the printer 20 are not limited to those described above. For example, inks such as light cyan (Lc), light magenta, orange, green, gray, light gray, white, metallic, Various liquids and inks such as a precoat liquid can be used.

The carriage mechanism 28 is controlled by the control unit 21 to move a carriage (not shown) included in the printer 20 from one end side to the other end side in the main scanning direction along the predetermined direction (main scanning direction) (and / or the other end side). From one end to the other). A print head 26 is mounted on the carriage, and the print head 26 moves by the carriage.
The feeding mechanism 29 is controlled by the control unit 21 and transports the recording medium in a feeding direction intersecting (orthogonal) with the main scanning direction by a roller (not shown) (see the recording medium G in FIG. 2).

  The head drive unit 27 is a piezoelectric device provided corresponding to each nozzle of the print head 26 based on print data (print data will be described later) acquired from the control device 10 by the control unit 21 via the I / F 25. A drive voltage for driving the element is generated. The head drive unit 27 outputs the drive voltage to the print head 26. The piezoelectric element is deformed when the driving voltage is applied, and ejects ink from the corresponding nozzle. As a result, the print head 26 that is moving by the carriage ejects ink (ink droplets) for each ink type from each nozzle to the recording medium. The ejected ink adheres to the recording medium, and “dots” are formed on the surface of the recording medium, whereby an image based on the print data is reproduced on the recording medium. A dot basically refers to ink that has landed on a recording medium. However, even before the ink has landed on the recording medium, the expression “dot” may be used for convenience of explanation.

The material used as the recording medium is typically paper, but various materials such as fiber, plastic, metal, and other natural and artificial materials are used in addition to paper.
The movement of the print head 26 from the one end side to the other end along the main scanning direction, or the movement from the other end side to the one end side is also referred to as main scanning or pass.

Further, the head driving unit 27 has an ejection abnormality detection means 27a for detecting an abnormal nozzle having an abnormality in ink ejection.
Furthermore, the printer 20 includes a display unit 30 configured by, for example, a liquid crystal display, and an operation unit 31 configured by, for example, a button or a touch panel. In the printer 20, the means for ejecting ink droplets from the nozzles is not limited to the piezoelectric element, and means for ejecting ink droplets from the nozzles by heating ink with a heating element may be employed.

FIG. 2 simply illustrates the configuration of the print head 26 in the printer 20. The left side of FIG. 2 illustrates an array of nozzles Nz on the ink ejection surface 26a of the print head 26. The ink discharge surface 26a is a surface on which the nozzle Nz is opened, and is a surface facing the recording medium G when the print head 26 performs main scanning. The print head 26 has a nozzle row NL for each ink color (for example, CMYK) to be ejected. The nozzle row NL is a row in which the nozzles Nz are arranged at equal intervals along the feed direction, and in the example of FIG. 2, four nozzle rows NL are provided in parallel. In addition to being ejected by one nozzle row NL, one color of ink may be ejected by, for example, a plurality of nozzle rows NL that are arranged shifted in the feed direction.
In the present specification, even if the directions and positions of each component are expressed as orthogonal, horizontal, equidistant, parallel, etc., they mean only strictly orthogonal, horizontal, equidistant, and parallel. Instead, it also includes an error that is acceptable in terms of product performance and an error that may occur during product manufacture.

2. First Embodiment A first embodiment will be described based on the above-described configuration.
FIG. 3 is a flowchart showing processing (print control processing) in which the control device 10 causes the printer 20 to execute printing in accordance with the printer driver PD.
In step S100, the control unit 11 acquires image data arbitrarily selected by the user from a predetermined input source. A user can arbitrarily select image data representing an image to be printed on a recording medium by operating the operation unit 18 or the like while visually recognizing a user interface screen (UI screen) displayed on the display unit 17 or the like. it can. The input source of the image data is not particularly limited. For example, in addition to the HDD 16, a memory card (not shown) inserted from the outside into the control device 10 or the printer 20, any image input connected to be able to communicate with the control device 10. Applicable to the device.

  The image data acquired in step S100 is, for example, in a bitmap format, and the density of element colors such as R (red), G (green), and B (blue) is set to gradation (for example, 0 to 255) for each pixel. 256 gradation) expressed RGB data. In addition, when the acquired image data does not correspond to such an RGB color system, the control unit 11 converts the acquired image data into data of the color system. Furthermore, the control unit 11 appropriately performs resolution conversion processing for matching the print resolution in the main scanning direction and the feeding direction of the printer 20 with respect to the image data.

  In step S110, the control unit 11 performs a color conversion process on the image data after step S100. That is, the color system adopted by the image data is converted into an ink color system (for example, CMYK) used by the printer 20 for printing. The color conversion process is executed for each pixel by referring to a color conversion table (lookup table) that preliminarily defines the conversion relationship of the color system. As described above, when the image data represents the color of each pixel with RGB, the RGB gradation value for each pixel is converted into the ink amount for each CMYK. Such CMYK values after color conversion are expressed stepwise by numerical values such as 0 to 100 (%), for example, and it can be said that the ink amount (density) in the corresponding pixel is expressed in gradation. Hereinafter, such image data expressed by CMYK values for each pixel is also referred to as “ink amount data”.

  In step S120, the control unit 11 performs halftone processing on the image data (ink amount data) after step S110 and converts the image data into print data. For example, the control unit 11 may execute halftone processing by dithering using a predetermined dither mask, or may execute halftone processing by an error diffusion method. By halftone processing, print data (dot data) in which ejection (with dots) or non-ejection (without dots) of each color ink of CMYK is determined for each pixel. In this case, the higher the ink amount value defined by a certain pixel in the ink amount data, the higher the possibility that ink ejection will be determined for that pixel as a result of the halftone process.

  In step S130, the control unit 11 rearranges the pixels constituting the print data (dot data) generated in step S120 in the order to be transferred to the print head 26 according to a predetermined rule for assignment to nozzles. With the rearrangement process, the dots defined by the pixels constituting the print data are transferred from any nozzle in the print head 26 according to the pixel position and ink color, in which pass, and at which timing in the pass. To determine whether or not to discharge. The print data after the rearrangement process according to the predetermined rule of the assignment is output to the printer 20 side via the I / F 19 (output process). As a result, the pixels constituting the print data are substantially assigned to one of the nozzles of the print head 26.

The printer 20 controls main scanning (pass) of the print head 26, ejection or non-ejection of ink from each nozzle, and feeding of the recording medium based on the print data input via the I / F 25, and in step S100. An image represented by the acquired image data is printed on a recording medium.
The control unit 11 performs the discharge of ink by the nozzles by assigning the pixels that constitute the image and have determined whether or not to discharge the ink to the nozzles in that the processes of steps S120 and S130 are performed. It can be said that it functions as a discharge control unit for controlling.

  In the present embodiment, the predetermined rule for the assignment is a pixel row having “abnormal nozzle corresponding pixels” that are pixels assigned to “abnormal nozzles” having abnormality in ink ejection among the nozzles of the print head 26. When the “adjacent pixel row”, which is a pixel row adjacent to the “nozzle-compatible pixel row”, is printed by a plurality of passes, the degree of dispersion of dots formed in one pass is set to a pixel row that is not an adjacent pixel row. It includes at least a rule of lowering the degree of dispersion of dots formed in one pass when printing is performed by a plurality of passes.

  First, the abnormal nozzle is a generic term for nozzles that cannot normally eject ink droplets (there is an ejection abnormality) even though the ejection operation is performed by applying the drive voltage. Possible causes of abnormal discharge include air bubbles entering the nozzle and the ink flow path communicating with the nozzle, drying and thickening (adhering) of ink near the nozzle, and paper dust adhering to the vicinity of the nozzle opening, etc. Is mentioned. When an ejection abnormality occurs, typically, ink droplets are not ejected from the nozzles, resulting in a phenomenon in which dots that should be originally formed on the recording medium are not formed (dot missing). Also, in the case of ejection failure, even if ink droplets are ejected from the nozzle, the amount of liquid is too small or the flight direction (ballistics) of the ink droplets shifts and does not land properly. Is likely to occur.

  In the present embodiment, the control unit 21 of the printer 20 stores the nozzle information NI (see FIG. 1) in, for example, an EEPROM (not shown). The nozzle information NI is information describing the presence or absence of ejection abnormality for each nozzle of the print head 26. The nozzle information NI may be anything as long as it is information that can directly or indirectly determine whether there is a discharge abnormality for each nozzle. In this embodiment, the process for generating the nozzle information NI is not particularly limited, and any known technique for determining and detecting nozzle ejection abnormality can be employed. For example, in the printer 20, the ejection abnormality detection unit 27 a determines the presence or absence of ejection abnormality for each nozzle using the method disclosed in Japanese Patent Laid-Open No. 2013-126676, and the control unit uses the result as nozzle information NI. 21 can be output. Specifically, ink was normally ejected from the nozzles by measuring the residual vibration waveform (period, etc.) of a so-called diaphragm that bends as the piezoelectric element is deformed by applying the drive voltage. It is determined whether there is a discharge abnormality. Alternatively, by artificially or automatically evaluating the presence or absence of missing dots in the test pattern printed by ejecting ink from each nozzle of the print head 26, the presence or absence of ejection abnormality for each nozzle is determined, and the determination result is The nozzle information NI may be written.

The process of assigning pixels to nozzles in step S130 will be described in detail.
FIG. 4 is a diagram for explaining the correspondence between the nozzles constituting the nozzle row NL and the pixels constituting the image data IM assigned to the nozzles. The correspondence relationship between the nozzles and the pixels shown in FIG. 4 is merely an example, and such a correspondence relationship is changed according to the printing method employed by the printer 20. On the left side of FIG. 4, for ease of explanation, nozzle rows NL corresponding to one ink color are assigned numbers 1 to 10 (nozzle numbers) from one end side to the other end side of the row. In addition, an example composed of 10 nozzles (circles) is shown. In FIG. 4, the position of one nozzle row NL (relative to the recording medium in the feed direction) for each pass (first pass, second pass, third pass, fourth pass,...) By the print head 26. This shows that the position of the target is changing. Actually, instead of the print head 26 moving in the feed direction, the recording medium is moved in the feed direction by a predetermined feed amount by the feed mechanism 29 each time the pass is completed. In the second and subsequent passes, the description of the nozzle number is omitted.

  On the right side of FIG. 4, the image data IM is illustrated as a set of a plurality of pixels (rectangular shapes) arranged in the X direction (corresponding to the main scanning direction) and the Y direction (corresponding to the feeding direction). In the image data IM, for example, the resolution in each of the X direction and the Y direction corresponds to the printing resolution (for example, 360 dpi × 360 dpi) in each of the main scanning direction and the feeding direction adopted by the printer 20. In FIG. 4, the numbers attached to the outside of the image data IM as 1, 2, 3... In the X direction and the Y direction indicate the positions (X, Y coordinates) of the respective pixels in the image data IM. The image data IM shown here refers to the print data (dot data) described above, but is interpreted as image data (RGB data) before color conversion processing or image data (ink amount data) after color conversion processing. Also good. In the example of FIG. 4, a number in a rectangle indicating a pixel means “nozzle number / pass number” to which the pixel is assigned. For example, a pixel indicated as “5/1” is a pixel assigned to the fifth nozzle in the first pass.

  In the example of FIG. 4, the interval (nozzle pitch) between the nozzles constituting the nozzle row NL corresponds to 180 nozzles / inch (npi), while the resolution in the Y direction of the image data IM is 360 dpi. is there. Therefore, by setting the feed amount of the recording medium after each pass to be 1.5 times the nozzle pitch, for example, the print resolution in the feed direction becomes 360 dpi. In the example of FIG. 4, multi-pass printing is shown in which the print head 26 completes printing of one “pixel row” in multiple passes (twice). In the present embodiment, the pixel row means a region where pixels having the same Y coordinate are continuous from one end to the other end of the image data in the X direction. The pixel column may be called a raster line. While the resolution in the X direction of the image data IM is 360 dpi, the print head 26 has the ability to set the print resolution in the main scanning direction by one pass to 360 dpi. Therefore, the print head 26 can theoretically print all the pixels constituting one pixel column in the image data IM with one pass and one nozzle.

  In step S130, the control unit 11 reads the nozzle information NI described above from the printer 20, and based on the nozzle information NI, for example, the sixth nozzle (the nozzle shown in gray in FIG. 4) has an ejection abnormality. That is, it is assumed that the sixth nozzle is recognized as an “abnormal nozzle”. In this case, the pixels assigned to the sixth nozzle are “abnormal nozzle corresponding pixels”, and when they are reproduced on the recording medium, even if ink is to be ejected, dots are actually missing.

  Based on the printing method already set for the printer 20, the control unit 11 specifies which pixel constituting the image data IM is an “abnormal nozzle corresponding pixel”. The printing method here refers to the printing resolution in each of the main scanning direction and the feeding direction, the feeding amount of the recording medium every time one pass described above, and the number of passes required to print one pixel row (2 Times), the behavior of the printer 20 determined by the contents of the nozzle usage rate defining mask 16a, and the like. Printing one pixel row in two passes means printing one pixel row with two nozzles. In the printing method according to the present embodiment, the use of two nozzles used for printing one pixel column (the preceding nozzle used in the preceding pass and the succeeding nozzle used in the succeeding pass among the two passes). The rate is assumed to be 1: 1.

  FIG. 5A illustrates the nozzle usage rate defining mask 16a, and FIG. 5B illustrates the nozzle usage rate defining mask 16b. The nozzle usage rate defining masks 16a and 16b are both matrices in which the vertical axis indicates the nozzle usage rate and the horizontal axis indicates the pixel position. More specifically, the nozzle usage rate on the vertical axis is the usage rate of the preceding nozzle for printing one pixel row. The total usage rate of each of the two nozzles for printing one pixel row is designed to be 100%. Therefore, the nozzle usage rate 80% defined by the nozzle usage rate defining masks 16a and 16b means that the usage rate of the preceding nozzle is 80% and the usage rate of the subsequent nozzle is 20%. “1” in the nozzle usage rate defining masks 16a and 16b indicates a pixel position where the preceding nozzle is used, and “0” indicates a pixel position where the succeeding nozzle is used.

  The difference between the nozzle usage rate defining mask 16a and the nozzle usage rate defining mask 16b is a difference in the degree of dispersion of pixel positions where the same nozzle is used. The nozzle usage rate defining mask 16a is a mask having a higher degree of dispersion than the nozzle usage rate defining mask 16b. For example, according to the nozzle usage rate 50% column of the nozzle usage rate defining masks 16a and 16b, the same number of pixel positions “1” where the preceding nozzle is used and “0” where the subsequent nozzle is used. In the nozzle usage rate defining mask 16a, the “1” and “0” are alternately arranged. On the other hand, in the nozzle usage rate defining mask 16b, the “1” and “0” are shared. “0” is relatively concentrated between the same values (having a certain degree of continuity).

  In the description related to the nozzle usage rate defining masks 16a and 16b, the expression “use” of the nozzle is used. This guarantees the actual use of the nozzle (the action of the nozzle ejecting ink). It doesn't mean. Whether or not the nozzle ejects ink depends on whether or not the pixel assigned to the nozzle is the “dotted” pixel. Therefore, the expression “use” of the nozzle in the description related to the nozzle usage rate defining masks 16a and 16b means that a pixel is assigned to the nozzle as an information process (regardless of the presence or absence of a dot).

  As described above, in the printing method of this embodiment, the usage rate of the preceding nozzle and the succeeding nozzle is set to 1: 1. Therefore, the control unit 11 refers to the nozzle usage rate 50% column of the nozzle usage rate defining mask 16a and alternately assigns each pixel to the preceding nozzle and the subsequent nozzle for each pixel column of the image data IM. As a result of such assignment, the control unit 11 can specify the pixel assigned to the sixth nozzle, which is an abnormal nozzle, as “abnormal nozzle corresponding pixel”. In FIG. 4, a part of the abnormal nozzle corresponding pixels assigned to the sixth nozzle which is an abnormal nozzle (pixels whose X coordinate is an odd number in the pixel row of Y = 3) is illustrated in gray. In the example of FIG. 4, the pixels constituting the pixel row of Y = 3 are alternately assigned to the sixth nozzle (leading nozzle) in the first pass and the third nozzle (following nozzle) in the third pass. It is done. In the example of FIG. 4, at least the pixel row with Y = 3 corresponds to the “abnormal nozzle corresponding pixel row”.

  Next, the control unit 11 identifies a pixel column adjacent in the Y direction before and after the pixel column having the abnormal nozzle corresponding pixel specified as described above (abnormal nozzle corresponding pixel column) as an “adjacent pixel column”. Then, the control unit 11 refers to the nozzle usage rate defining mask 16b instead of the nozzle usage rate defining mask 16a only for the adjacent pixel row, and the preceding nozzle used to print each pixel on the adjacent pixel row. Assign to the trailing nozzle. In FIG. 4, as an example of the adjacent pixel column, the Y = 2 pixel column and the Y = 4 pixel column adjacent to the Y = 3 abnormal nozzle corresponding pixel column are surrounded by a chain line.

  That is, as can be seen from the column of 50% nozzle usage rate of the nozzle usage rate defining mask 16b shown in FIG. 5B, in the adjacent pixel column, the pixels allocated to the preceding nozzle and the pixels allocated to the subsequent nozzle are respectively It continues to some extent. For example, in the pixel row of Y = 2, the pixels assigned to the fourth nozzle (previous nozzle) in the second pass are approximately four pixels in the X direction, and the first nozzle (following nozzle) in the fourth pass. ) Are assigned to about 4 pixels in the X direction. In the pixel row of Y = 4, the pixels assigned to the fifth nozzle (previous nozzle) in the second pass are continuous in about 4 pixels in the X direction, and the second nozzle (following nozzle) in the fourth pass. ) Are assigned to about 4 pixels in the X direction. Although omitted in FIG. 4, the nozzle usage rate defining mask 16b having a low degree of dispersion is also used for adjacent pixel rows adjacent to the abnormal nozzle corresponding pixel row other than the pixel row of Y = 3. Assignment of pixels to nozzles is performed.

  The effect by 1st Embodiment is demonstrated. When printing a certain pixel row by a plurality of passes, it is possible to improve the graininess in the printing result by dispersing dots formed in the same pass as much as possible. Therefore, basically, when assigning each pixel constituting the pixel row to any one of a plurality of passes (a plurality of nozzles), the assignment is performed according to the nozzle usage rate defining mask 16a having a high degree of dispersion. According to the first embodiment, for the adjacent pixel row adjacent to the pixel row having the abnormal nozzle corresponding pixel assigned to the abnormal nozzle, the nozzle usage rate defining mask 16b having a low degree of dispersion is applied at the time of the assignment. use. As a result, the pixels assigned to the preceding nozzle used in the preceding pass among the two passes for printing the adjacent pixel row are relatively continuous in the main scanning direction (also the pixels assigned to the succeeding nozzle). Is relatively continuous in the main scanning direction).

  That is, in the print result of the adjacent pixel row, the continuity of dots formed in one pass is high when compared with the print result of the pixel row that is not the adjacent pixel row. A plurality of dots that are continuously formed at almost the same time (within the same pass period) interfere with each other and bleed after landing on the recording medium and drying, as compared to a case where the dots are formed in a dispersed manner. Easy (easy to spread). Accordingly, dot missing due to abnormal nozzles in which ejection abnormality such as clogging is observed is formed continuously in one pass corresponding to adjacent pixel rows (at least partially in contact with each other). It is eroded by the blurred dots, and as a result, the missing dots are hardly visually recognized.

  The present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following embodiments and modifications can be employed. A configuration in which each embodiment or modification example is appropriately combined also falls within the disclosure scope of the present invention. In the description of the following embodiments and modifications, descriptions of matters common to the first embodiment will be omitted as appropriate.

3. Second Embodiment FIG. 6 is a diagram for explaining a correspondence relationship between nozzles constituting the nozzle row NL and pixels constituting image data IM assigned to the nozzles in the second embodiment. On the left side of FIG. 6, a nozzle row NL corresponding to one ink color has 12 nozzles (circles) numbered 1 to 12 (nozzle numbers) from one end side to the other end side of the row. ). In FIG. 6, as in FIG. 4, the position of one nozzle row NL (recording in the feeding direction) for each pass (first pass, second pass, third pass, fourth pass...) By the print head 26. It shows that the relative position with respect to the medium changes. In the second and subsequent passes, the description of the nozzle number is omitted. Further, in FIG. 6, the usage rate of the nozzle is shown for reference in a circle representing the nozzle.

  On the right side of FIG. 6, as in FIG. 4, the image data IM is illustrated as a set of a plurality of pixels (rectangles) arranged in the X direction and the Y direction. The meanings of the numbers attached to the outside of the image data IM as 1, 2, 3... In the X direction and the Y direction, respectively, and the meanings of the numbers in the rectangles indicating the pixels are the same as in the description of FIG. The example of FIG. 6 shows multi-pass printing in which the print head 26 completes printing of one pixel row in four passes. Specifically, the printer 20 prints odd-numbered pixels whose X-coordinates in one pixel column are odd (X = 1, 3, 5,...) In two passes, and the X-coordinates in the pixel column are even ( Even-numbered pixels with X = 2, 4, 6,...) Are printed in another two passes.

  In such a printing method according to the second embodiment, the nozzle used in the preceding pass among the two passes for printing odd pixels in one pixel column is the first preceding nozzle, and printing of the odd pixels is performed. The nozzle used in the subsequent pass for the purpose is referred to as a first subsequent nozzle. Further, the nozzle used in the preceding pass among the two passes for printing the even pixels in the one pixel column is used as the second preceding nozzle, and used in the subsequent pass for printing the even pixels. This nozzle is called the second trailing nozzle. Further, the usage rate of the first preceding nozzle and the first succeeding nozzle (ratio of the number of pixels allocated to the first preceding nozzle and the first succeeding nozzle) is not necessarily 1: 1, and similarly, the second leading nozzle The usage rate of the nozzle and the second succeeding nozzle (ratio of the number of pixels allocated to the second preceding nozzle and the second succeeding nozzle) is not necessarily 1: 1.

  For example, when paying attention to the pixel row of Y = 1, odd pixels are assigned to the 11th nozzle (first preceding nozzle) in the first pass and the fifth nozzle (first following nozzle) in the fifth pass. However, the usage rate of the first preceding nozzle and the usage rate of the first succeeding nozzle that are paired for printing odd-numbered pixels in the same pixel row are not equal to each other (however, the usage rate is 100% in total). The even pixels in the pixel row with Y = 1 are assigned to the eighth nozzle (second leading nozzle) in the third pass and the second nozzle (second trailing nozzle) in the seventh pass. As described above, the usage rate of the second preceding nozzle and the usage rate of the second subsequent nozzle that are paired for printing even-numbered pixels in the same pixel row are not equal (however, the total is 100%).

  That is, in step S130, the control unit 11 refers to the column corresponding to the usage rate of the preceding nozzle (first preceding nozzle) in the nozzle usage rate defining mask 16a having a high degree of dispersion as shown in FIG. 5A, for example. The odd pixels for each pixel column of the image data IM are assigned to the first preceding nozzle and the first following nozzle. Similarly, the control unit 11 refers to the column corresponding to the usage rate of the preceding nozzle (second preceding nozzle) in the nozzle usage rate defining mask 16a, and for those even pixels for each pixel column of the image data IM, Are assigned to the second preceding nozzle and the second succeeding nozzle. Taking the pixel row of Y = 1 as an example, 20% of the odd-numbered pixels are assigned to the 11th nozzle (first preceding nozzle) in the first pass, and the remaining 80% are assigned to the 5th pass. Assigned to the fifth nozzle (first trailing nozzle). Further, 80% of the even pixels in the Y = 1 pixel row are allocated to the eighth nozzle (second preceding nozzle) in the third pass, and the remaining 20% are the second pixel in the seventh pass. Nozzles (second trailing nozzles).

  In step S130, the control unit 11 reads the nozzle information NI described above from the printer 20, and based on the nozzle information NI, for example, the eighth nozzle (the nozzle shown in gray in FIG. 6) is “abnormal nozzle”. Suppose you recognize it. In this case, the pixel assigned to the eighth nozzle is the “abnormal nozzle corresponding pixel”. As a result of assigning each pixel of the image data IM to the nozzle, the control unit 11 can identify the pixel assigned to the eighth nozzle that is an abnormal nozzle as “abnormal nozzle corresponding pixel”. In FIG. 6, a part of pixels corresponding to the abnormal nozzle assigned to the eighth nozzle which is an abnormal nozzle (80% of the even pixels in the pixel row of Y = 1, and “ The pixel whose position is specified in accordance with the “nozzle usage rate 80%” column is illustrated in gray. In the example of FIG. 6, at least a pixel row of Y = 1 having such an abnormal nozzle corresponding pixel corresponds to an “abnormal nozzle corresponding pixel row”.

  As in the first embodiment, the control unit 11 identifies a pixel column adjacent to the abnormal nozzle corresponding pixel column in the Y direction as an “adjacent pixel column”. Then, the control unit 11 refers to the nozzle usage rate defining mask 16b having a low degree of dispersion, not the nozzle usage rate defining mask 16a, and prints each pixel on the adjacent pixel row only in the adjacent pixel row. Assign to the nozzle to be used. In FIG. 6, as an example of the adjacent pixel column, the Y = 2 pixel column adjacent to the Y = 1 abnormal nozzle corresponding pixel column is surrounded by a chain line. In the second embodiment, if the abnormal nozzle corresponding pixel is an odd pixel, the control unit 11 performs allocation to the nozzle with reference to the nozzle usage rate defining mask 16b for the odd pixel in the adjacent pixel row, and the abnormal nozzle If the corresponding pixel is an even pixel, the allocation to the nozzle is executed with reference to the nozzle usage rate defining mask 16b for the even pixel in the adjacent pixel row.

  The abnormal nozzle corresponding pixels included in the Y = 1 abnormal nozzle corresponding pixel row are even pixels. For this reason, the control unit 11 refers to the nozzle usage rate defining mask 16b when assigning even-numbered pixels to nozzles in the adjacent pixel row (pixel row of Y = 2). As a result, as illustrated in FIG. 6, 40% of the even-numbered pixels in the pixel row with Y = 2 (pixels shown in gray in the adjacent pixel row surrounded by the chain line) are the second preceding nozzle (second pass). When the remaining 60% is allocated to the second succeeding nozzle (fourth nozzle in the sixth pass), it is compared with the case of referring to the nozzle usage rate defining mask 16a. In this arrangement, the pixels assigned to the second preceding nozzle are concentrated and the pixels assigned to the second subsequent nozzle are concentrated. Although omitted in FIG. 6, the nozzle usage rate defining mask 16b having a low degree of dispersion is used in the adjacent pixel row adjacent to the abnormal nozzle corresponding pixel row other than the pixel row where Y = 1. Assignment of pixels to nozzles is performed.

  Also in the second embodiment, the effect according to the first embodiment is achieved. That is, according to the second embodiment, in the adjacent pixel row adjacent to the pixel row having the abnormal nozzle corresponding pixel assigned to the abnormal nozzle, one of the odd pixel and the even pixel adjacent to the abnormal nozzle corresponding pixel. Among the two passes for printing the pixels of, pixels assigned to the preceding nozzle (first preceding nozzle or second preceding nozzle) used in the preceding pass are relatively gathered in the main scanning direction, Pixels assigned to the succeeding nozzle (first succeeding nozzle or second succeeding nozzle) used in the succeeding pass are relatively gathered in the main scanning direction. Thereby, in the printing result of the adjacent pixel row, the degree of dispersion between dots formed in some passes is low when compared with the printing result of the pixel row that is not the adjacent pixel row. Accordingly, even if the number of dots formed in the same pass corresponding to the adjacent pixel row is not as large as in the first embodiment, even in the second embodiment, the missing dot due to the abnormal nozzle is visually recognized to some extent. It can be said that it becomes difficult to be done.

4). Modified example Modified example 1:
In step S130, the control unit 11 analyzes the print data (dot data) generated by the halftone process in step S120, and there is an abnormal nozzle corresponding pixel for which ink ejection (with dots) is determined in the print data. It is determined whether or not. Then, when there is an abnormal nozzle corresponding pixel for which ink ejection has been determined, the control unit 11 performs the adjacent pixel adjacent to the pixel row having the abnormal nozzle corresponding pixel (abnormal nozzle corresponding pixel row) as described above. Each pixel may be assigned to the preceding nozzle and the succeeding nozzle using the nozzle usage rate defining mask 16b. For example, when there is an abnormal nozzle corresponding pixel for which dot ejection has been determined by the halftone processing in step S120 in the Y = 3 pixel row (abnormal nozzle corresponding pixel row) of the image data IM shown in FIG. As long as each pixel constituting the pixel row of Y = 2 and the pixel row of Y = 4 is assigned to the preceding nozzle and the succeeding nozzle with reference to the nozzle usage rate defining mask 16b instead of the nozzle usage rate defining mask 16a .

  According to the first modification, after confirming that there is a dot to be formed by the abnormal nozzle, printing is performed by a plurality of passes for the adjacent pixel column including the pixel corresponding to the abnormal nozzle that defines the dot. Pixels are assigned to nozzles so as to reduce the degree of dispersion of dots formed in one pass. Accordingly, it is possible to generate dot bleeding corresponding to the vicinity (adjacent pixel row) of the position where dot missing occurs, and to reliably compensate for dot missing due to an abnormal nozzle. In addition, when there is no dot to be formed by the abnormal nozzle in the first place, it is possible to avoid a situation in which the dot blur is unnecessarily generated in correspondence with the adjacent pixel row.

  A method for determining “whether there is an abnormal nozzle corresponding pixel for which ink ejection has been determined” by the control unit 11 in Modification 1 will be described. In the abnormal nozzle corresponding pixel row, the control unit 11 determines that the abnormal nozzle for which ink ejection has been determined when the number or ratio of the pixels for which ink ejection has been determined in the halftone process in step S120 is equal to or greater than a predetermined threshold. It can be determined that there is a corresponding pixel. For example, the control unit 11 determines that ink ejection is determined by J (where 1 ≦ J <I) or more abnormal nozzle corresponding pixels out of the number I of abnormal nozzle corresponding pixels included in one abnormal nozzle corresponding pixel row. If there is an abnormal nozzle corresponding pixel column, it is determined that there is an abnormal nozzle corresponding pixel for which ink ejection has been determined. Alternatively, when the ink ejection is determined at a predetermined percentage or more of the number of abnormal nozzle corresponding pixels constituting one abnormal nozzle corresponding pixel row, the control unit 11 determines the ink discharge to the abnormal nozzle corresponding pixel row. It is determined that there is an abnormal nozzle corresponding pixel.

In addition, after determining that there is an abnormal nozzle corresponding pixel for which ink ejection has been determined, the “adjacent pixel row” can be interpreted as follows, for example.
FIG. 7 is a diagram for explaining adjacent pixel columns. 7A and 7B both illustrate a pixel row corresponding to an abnormal nozzle and a pixel row adjacent to the front and rear in the Y direction of the pixel row corresponding to the abnormal nozzle. In FIG. 7A and FIG. 7B, one pixel column is printed in two passes, and the pixels shown in gray in the abnormal nozzle corresponding pixel column are the abnormal nozzle corresponding pixels. In the abnormal nozzle corresponding pixel row, “1” indicates a pixel for which ink ejection has been determined by the halftone process in step S120, and “0” indicates a pixel for which ink non-ejection has been determined by the halftone process. .

  For example, as illustrated in FIG. 7A, the control unit 11 sets the entire pixel row (pixels hatched in FIG. 7A) adjacent to the front and rear of the abnormal nozzle corresponding pixel row having the abnormal nozzle corresponding pixels for which ink ejection has been determined as adjacent pixels. It is also possible to grasp the data as a column and execute allocation to the nozzle with reference to the nozzle usage rate defining mask 16b for each pixel constituting the adjacent pixel column. Alternatively, for example, as illustrated in FIG. 7B, the control unit 11 selects a pixel (Y direction) adjacent to the abnormal nozzle corresponding pixel for which ink ejection has been determined among the pixels constituting the pixel array adjacent to the front and rear of the abnormal nozzle corresponding pixel row. Alternatively, a set of pixels adjacent to each other diagonally (hatched pixels in FIG. 7B) is grasped as an adjacent pixel column, and each pixel constituting such an adjacent pixel column is referred to the nozzle usage rate defining mask 16b. The assignment to may be performed. In the case of FIG. 7B, the control unit 11 refers to the nozzle usage rate defining mask 16 a for the pixels that constitute the pixel rows that are adjacent to the pixel row adjacent to the abnormal nozzle corresponding pixel row, with reference to the nozzle usage rate defining mask 16 a. Perform assignment to.

Modification 2:
When ink is ejected continuously by one nozzle, the shorter the time interval for ejecting ink, the more easily the inks that have landed on the recording medium interfere with each other and spread. Therefore, it can be said that there is a certain correlation between the printing resolution and the ease of ink bleeding. More specifically, it can be said that if the printing resolution is high, the effect of filling in the neighboring blanks is enhanced (if the printing resolution is low, the effect of filling in the neighboring blanks is diminished). Therefore, as the printing resolution in the main scanning direction is lower, the control unit 11 decreases the degree of dispersion of dots formed in a single pass when printing adjacent pixel rows by a plurality of passes.

  The user can select and set the print resolution for the printer 20 by operating the operation units 18 and 31 and the like. For example, it is assumed that the printer 20 can achieve at least a first print resolution and a second print resolution that is higher than the first print resolution as the print resolution in the main scanning direction. When the first print resolution is set as the print resolution in the main scanning direction, the control unit 11 passes the adjacent pixel row a plurality of times as compared with the case where the second print resolution is set. The assignment of pixels and nozzles is executed so as to reduce the degree of dispersion of dots formed in one pass when printing.

  In the first embodiment, by referring to the nozzle usage rate defining mask 16b, the pixels printed in the same pass among the pixels constituting the adjacent pixel row are continuously arranged by about 4 pixels at the maximum (formed in the same pass). The dots are continuous for a maximum of about 4 dots in the main scanning direction). In the second modification, the control unit 11 performs such control that makes about four dots continue in the adjacent pixel row when the first print resolution is set as the print resolution in the main scanning direction.

  On the other hand, when the second print resolution is set as the print resolution in the main scanning direction, the control unit 11 has a higher degree of dispersion than the nozzle use rate defining mask 16b (however, than the nozzle use rate defining mask 16a). Refers to the third nozzle usage rate defining mask. By referring to such a third nozzle usage rate defining mask, pixels that are printed in the same pass among the pixels constituting the adjacent pixel column are, for example, continuously about 2 to 3 pixels at maximum (formed in the same pass). The control is executed so that a maximum of two or three dots are continuously arranged in the main scanning direction. According to the second modified example, it is possible to realize ink bleeding in an adjacent pixel row that is optimal for compensating for missing dots due to abnormal nozzles in accordance with the printing resolution in the main scanning direction.

Modification 3:
If the recording medium used for printing has the characteristic that ink is likely to bleed, it can be said that the effect that the landed ink fills the blank in the vicinity is enhanced. Therefore, the control unit 11 decreases the degree of dispersion of dots formed in one pass when printing adjacent pixel rows by a plurality of passes so that the ink is less likely to spread on the recording medium.

  The user can arbitrarily select and set a recording medium from various recording media such as glossy paper and plain paper for the printer 20 by operating the operation units 18 and 31. Here, the printer 20 includes at least a first recording medium (for example, glossy paper) that is a certain type of paper, and a second recording medium (for example, plain paper) having a characteristic that ink is more likely to bleed than the first recording medium. And can be used for printing. Then, when the first recording medium is set as the recording medium, the control unit 11 can print the adjacent pixel columns in a plurality of passes, compared to the case where the second recording medium is set. Allocation of pixels and nozzles is executed so as to reduce the degree of dispersion of dots formed in one pass.

  As an example, the control unit 11 performs the control of making dots formed in the same pass in the adjacent pixel row as described above continuously in a maximum of about 4 dots in the main scanning direction, and the first recording medium is set as the recording medium. Execute if there is. On the other hand, when the second recording medium is set as the recording medium, the control unit 11 sets the dots formed in the same pass in the adjacent pixel row as described above to a maximum of about a few dots in the main scanning direction. Execute the control to be continued. According to the third modified example, the density of dots formed in the same pass in the adjacent pixel row that is optimal for compensating for the missing dot due to the abnormal nozzle according to the characteristics of the recording medium (easy to spread ink). A degree can be realized.

Modification 4:
The control unit 11 may switch the degree of dispersion of dots formed in the same pass in the adjacent pixel rows in accordance with the color of ink used by the printer 20. For example, ink having a relatively low density (inks such as Y and Lc) has a low effect of making adjacent blanks inconspicuous even if dots formed in the same pass are densely packed. Therefore, the print head 26 can discharge at least the first ink having a relatively low density and the second ink (ink such as K) having a higher density than the first ink. When printing a row by a plurality of passes, the degree of dispersion of the dots of the second ink formed in one pass is made lower than the degree of dispersion of the dots of the first ink formed in one pass.

  As an example, the control unit 11 controls the second ink pixel (the second ink pixel (for example) to make dots formed in the same pass in the adjacent pixel row as described above continuously in the main scanning direction at a maximum of about 4 dots or a few dots. This is executed for pixels that constitute print data after halftone processing and that define dot ejection / non-ejection for the second ink. On the other hand, the control unit 11 adjoins the pixel of the first ink (the pixel constituting the print data after the halftone process and defining the dot ejection / non-ejection of the first ink). Regardless of whether or not it belongs to a pixel column, pixel allocation is performed with reference to the nozzle usage rate defining mask 16a having a high degree of dispersion. According to the fourth modification, only dots that are formed in the same pass in the adjacent pixel rows are only used for ink that has a high effect of making adjacent blanks (dot missing due to abnormal nozzles) inconspicuous by expanding bleeding. Make it dense. Therefore, the frequency of switching the nozzle usage rate defining mask is reduced, and the processing burden on the control unit 11 can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Print control system, 10 ... Control apparatus, 11 ... Control part, 12 ... CPU, 13 ... ROM, 14 ... RAM, 16 ... HDD, 16a, 16b ... Nozzle usage rate regulation mask, 17 ... Display part, 18 ... Operation , 19 ... I / F, 20 ... printer, 21 ... control unit, 22 ... CPU, 23 ... ROM, 24 ... RAM, 25 ... I / F, 26 ... print head, 26a ... ink ejection surface, 27 ... head drive , 27a: Discharge abnormality detection means, 28: Carriage mechanism, 29 ... Feed mechanism, 30 ... Display unit, 31 ... Operation unit, G ... Recording medium, IM ... Image data, NI ... Nozzle information, NL ... Nozzle array, Nz ... Nozzle, PD ... Printer driver

Claims (7)

A print control apparatus for controlling a printing process for forming dots of the ink on a recording medium by causing a print head to perform a scan for ejecting ink from a nozzle along with movement in a predetermined direction,
An ejection control unit that controls ejection of ink by the nozzles by allocating pixels that constitute an image and determined to eject or not eject the ink to the nozzles;
The ejection control unit scans an adjacent pixel row, which is a pixel row adjacent to a pixel row having an abnormal nozzle corresponding pixel, which is a pixel assigned to an abnormal nozzle having an abnormality in ink ejection among the nozzles, a plurality of times. The degree of dispersion of the dots formed in one scan when printing is performed according to the degree of dispersion of the dots formed in one scan when printing a pixel row that is not the adjacent pixel row by a plurality of scans. A printing control apparatus characterized by lowering the degree of dispersion.   The ejection control unit reduces the degree of dispersion of the dots formed by one scan when the adjacent pixel row is printed by a plurality of scans as the printing resolution by the scan is lower. The printing control apparatus according to claim 1.   The ejection control unit reduces the degree of dispersion of the dots formed in one scan when the adjacent pixel row is printed by a plurality of scans, such that the ink is less likely to spread on the recording medium. The print control apparatus according to claim 1, wherein the print control apparatus is a print control apparatus. The print head is capable of discharging at least a first ink and a second ink having a higher concentration than the first ink;
When the adjacent pixel row is printed by the plurality of scans, the ejection control unit determines the degree of dispersion of the dots of the second ink formed by one scan and the first scan formed by one scan. The printing control apparatus according to claim 1, wherein the printing control apparatus reduces the degree of dispersion of one ink dot.   When the ejection control unit determines the ejection of the ink to the abnormal nozzle corresponding pixel, the dots of the dots formed by one scan when the adjacent pixel row is printed by a plurality of scans. The degree of dispersion is lower than the degree of dispersion of the dots formed by one scan when printing a pixel row that is not the adjacent pixel row by a plurality of scans. Item 5. The print control apparatus according to any one of Items 4 to 7.   2. The state in which at least a part of the dots formed by the one scan are in contact with each other by reducing a dispersion degree of the dots formed by the one scan. The printing control apparatus according to claim 5. A printing control method for controlling a printing process for forming dots of the ink on a recording medium by causing a print head to perform a scan for ejecting ink from a nozzle along with movement in a predetermined direction,
A discharge control step of controlling the discharge of ink by the nozzles by allocating the pixels constituting the image and determined to discharge or not discharge the ink to the nozzles;
In the ejection control step, the scanning is performed a plurality of times on an adjacent pixel row that is a pixel row adjacent to a pixel row having an abnormal nozzle corresponding pixel that is a pixel assigned to an abnormal nozzle having an abnormality in ink ejection among the nozzles. The degree of dispersion of the dots formed in one scan when printing is performed according to the degree of dispersion of the dots formed in one scan when printing a pixel row that is not the adjacent pixel row by a plurality of scans. A printing control method characterized by lowering the degree of dispersion.